This invention relates to conduits and ducts for air handling equipment such as heating and air conditioning units. It is particularly concerned with a plenum starter piece.
In the heating and air conditioning field, there are many instances when it is necessary to connect a generally tubular conduit into an opening in a generally planar surface. A most typical instance is the attachment of conduit to the plenum of a furnace or air conditioner. For this reason the present invention is denominated a "plenum starter piece" although it should be understood that it may be employed to attach conduit to planar surfaces which are not parts of a plenum.
Various methods have been used in the past for attaching conduits to plenums, but one of the most common involves cutting a hole in the plenum wall which is approximately round, and installing a starter piece which consists of a short cylindrical tube having a series of outwardly bent tabs encircling one end thereof. Alternate tabs are placed on the interior of the plenum wall and the intervening tabs on the exterior of the wall. This, and other commonly employed methods have the disadvantages that installation is difficult and time consuming, the joint tends to be leaky, and the relative weakness of the joint makes it impractical to rely upon the plenum wall as a major means of support for a run of conduit.